1. Field of the Invention
The present invention relates to a linear motion guide unit in which a sliding element movable on a rail track in a linearly sliding manner is provided therein with lubricating plate assemblies.
2. Description of the Prior Art
The recently remarkable development in mechatronics technology increasingly requires linear motion guide units improved in precision, speed and miniature and the use of such apparatus extends into many technical fields. The linear motion guide units are extensively incorporated in reciprocating apparatus, which is in general employed in semiconductor manufacturing apparatus, inspection instruments, industrial robots and the like. The linear motion guide units recently become required to meet with needs of maintenance-free as well as high precision, high speed and miniature. To cope with the needs, the linear motion guide unit has required the self-lubrication of long service life on its relatively movable sliding areas.
A conventional linear motion guide unit, as shown in FIG. 20, has a track rail 2 and a sliding element, or slider 1, saddling the track rail 2. The track rail 2 is formed on lengthwise side surfaces 3 thereof with raceway grooves 4 and the slider 1 may move on the track rail 2 by virtue of rolling elements 7 running through the raceway groove 4. The track rail 1 has on lengthwise upper surface 14 thereof openings 13 spaced from each other. The track rail 2 is fixed to a mounting base 20 such as beds, platforms, working tables or the like by screwing bolts through the openings 13 of the track rail 2 and matching openings in the mounting base 20. The slider 1 has a casing 5 movable with respect to the track rail 2, and end caps 6 attached to the opposing ends of the casing 5. Provided on the upper surface of the casing 5 are openings 19 for fixture, by which other appliances, parts, chucks, grasping jaws or the like are mounted on the slider 1. Both the casing 5 and end caps 6 are formed on the lower surfaces thereof with recesses 10 by which the casing 5 and end caps 6 may saddle track rail 2 for free movement. The recesses 10 are each formed with raceway grooves 9 in opposition to the raceway grooves 4 on the track rail 2. The rolling elements 7, are confined for free movement in loaded raceways defined between the confronting raceway grooves 4 and 9. Retainer bands 18 are provided in the casing 5 so as to embrace the rolling elements 7 to thereby prevent the rolling elements 7 from falling out of the casing 5. Bottom seals 8 are secured to the lower surfaces of the slider 1 for closing clearances between the track rail 2 and slider 1.
The end caps 6 are provided therein with turnarounds for circulating the rolling elements 7. Mounted on the end caps 6 are end seals 17 for ensuring the sealing performance between the track rail 2 and the lengthwise opposing ends of slider 1. The end caps 6 and end seals 17 are secured to the opposing ends of the casing 5 by means of screws 16. The raceways defined by the confronting raceway grooves 4, 9, turnarounds formed in the end caps 6 and return passages 12 formed in parallel with the raceway grooves 9 in the casing 5, in combination, constitute endless-circulating paths for the rolling elements 7. Even though the rolling elements 7 are under loaded condition in the raceways, rolling-contact of the rolling elements 7 with the raceway grooves 4, 9 may help ensure the smooth movement of the slider 1 relative of the track rail 2.
To lubricate the relative sliding ways in the linear motion guide unit constructed as described above, grease or lubricating oil is usually employed. In case of grease, it is applied to the relative sliding ways through grease nipples 11. In contrast, lubricating oil is supplied to the sliding ways through pipe joints, which are used substituting for the grease nipples.
Japanese Patent Laid-Open No. 53637/1997 discloses a linear motion guide unit having for its object to provide a maintenance-free lubrication system. In the linear motion guide unit cited above, a reinforcing plate, lubricant-containing member and side seals, overlaid one on another in the order mentioned just above, are attached over each outer end surface of the end caps. The reinforcing plate is of steel plate that is formed into a substantially inverted U-shape, which is fit to the outward contour of the end cap and makes no contact with the track rail. The lubricant-containing member is also formed into a substantially inverted U-shape, which is fit to the contour of the end cap. The lubricant-containing member is provided on the inside thereof with convex portions, which are formed in adaptation with the cross section of the track rail so as to make the sliding contact with the upper and side surfaces of the track rail. For constant supply of the lubricant to the track rail, the convex portions of the lubricant-containing member are forced against the raceway grooves on the track rail by means of, for example, ring members inserted in holes formed in the lubricant-containing member, or by making the lubricant-containing member itself from elastic material. Pressing the lubricant-containing members against the raceway grooves on the track rail, however, renders the frictional force greater, resulting in causing the high frictional resistance adverse to the smooth movement of the slider.
Disclosed in Japanese Patent Laid-Open No. 200362/1996 is a linear motion guide unit having a sliding element that has fixed by clamping on end surfaces thereof with sealing means in which a lubricant-containing polymer member of the mixture of olefinic polymer with lubricant is adhered integrally to a polyolefin resin layer on a reinforcing plate. The lubricant-containing member is manufactured by the steps of melting the mixture of olefinic polymer with poly (xcex1-olefin) oil or the like, pouring the mixture into a mould and solidifying the molded mixture by cooling under pressure. In the prior art described above, it is very hard to bond together the lubricant-containing polymer member with the reinforcing plate of core metal, because much oil in the lubricant-containing polymer member is present on the confronting surfaces to be bonded together. Moreover, olefinic polymer for the lubricant-containing polymer member is inherently unsusceptible to bonding with other materials. The lubricant-containing polymer member of olefin polymer should be integrated with the reinforcing plate made of only the same olefinic resins susceptible to olefinic polymer, or integrally fused with an olefinic polymer coating over the metal plate.
Japanese Patent Laid-Open No. 205534/1998 discloses a linear motion guide unit that comprises a sliding element movable on a track rail formed with raceway grooves, the sliding element being composed of a casing formed with raceway grooves, rolling elements running through between the confronting raceway grooves, end caps arranged on end surfaces of the casing, lubricating plates arranged on the end caps, and end seals secured on the lubricating plates. The lubricating plates are each composed of a sintered resinous member having porous structure immersed with lubricating oil. The lubricating plates are urged against the raceway grooves on the track rail by elastic actions of metallic frames covering around the peripheries of the lubricating plates.
If the lubricant in the lubricant-containing member might be applied to the raceway grooves on the track rail in the linear motion guide unit with no urging the lubricating plates against the raceway grooves by the action of the external force, the sliding resistance between the lubricant-containing members and the raceway grooves on the track rail may be reduced remarkably while the lubricant-containing members may be kept from wear owing to the sliding contact of the lubricant-containing members relatively of the track rail. However, even if the lubricant-containing members are free from such urging force towards the track rail, the lubricant-containing members of porous structure are insufficient in resistance against deformation. It is, therefore, desired to use a core plate high in stiffness to thereby prevent the lubricant-containing member from the deformation while supply the lubricant to the raceway grooves with sure reliability.
The present invention has for its primary object to overcome the problems in the prior art as described above, and to provide a linear motion guide unit in which the lubricant-containing members to lubricate the raceway grooves are kept in substantial contact with the raceway grooves while kept from mechanical deformation, notwithstanding that no lubricant-containing member is urged against the raceway groove by the action of the external force such as elastic biasing force or the like, whereby the sliding element may move smoothly and the lubricant-containing members are kept against wear due to the movement of the sliding element relatively of the track rail and also prevented from clogging up.
The present invention relates to a linear motion guide unit comprising a track rail provided at lengthwise side surfaces thereof with first raceway grooves, a sliding element movable on the track rail, wherein the sliding element has a casing provided with second raceway grooves in opposition to the first raceway grooves, rolling elements movable along raceways defined between the confronting first and second raceway grooves, end caps secured to the opposing end surfaces of the casing, lubricating plate assemblies secured on the end caps, and end seals arranged on the ends of the lubricating plate assemblies, and further wherein the lubricating plate assemblies each have a core metal and a lubricant-containing member fixed on the core metal with adhesives or mechanical means, the lubricant-containing member being made of a sintered resinous component having porous structure immersed with lubricant.
According to one aspect of the present invention, the core metals have rigidity sufficient to protect the lubricant-containing members from deformation, so that the lubricant-containing members are released from undue urging forces, which have the tendency to forcibly bias the lubricant-containing members against the raceway grooves on the track rail, or make the lubricant-containing members deform to come apart away from the raceway grooves, thereby resulting in keeping the highly accurate sliding contact relation of the lubricant-containing members with the raceway grooves on the track rail as well as helping ensure the reliable lubricant supply to the raceway grooves.
The sintered resinous components for the lubricant-containing members each are of sintered high molecular porous body that is formed by heating powdery ultrahigh molecular weight synthetic resin in a design mould under pressure. The powdery synthetic resin used is selected from polyethylene, polypropylene, tetrafluoroethylene polymer and the like. The powdery ultrahigh molecular weight polyethylene is a material preferable for producing the molded article with high accuracy and further the resultant sintered resinous components are superior in wear proof and in adhesion to metals. In the lubricant-containing members made from the sintered resinous component of ultrahigh molecular weight synthetic resin, no urging force may be necessary for pressing the lubricant-containing members against the raceway grooves.
In case where the adhesives are used to fix the sintered resinous components onto the core metals, the immersion in the lubricant must be made after the sintered resinous components have been adhered to the core metals, because oily surfaces of the lubricant-containing members make much difficult the adhesion of the members to the core metals.
The lubricant-containing members fixed to the core metals of high rigidity with mechanical means may be protected from deformation owing to any external forces. Thus, the lubricant-containing members are released from undue urging forces, which have the tendency to forcibly bias the lubricant-containing members against the raceway grooves on the track rail, or make the lubricant-containing members deform to come apart away from the raceway grooves, thereby resulting in keeping the highly accurate sliding contact relation of the lubricant-containing members with the raceway grooves on the track rail as well as helping ensure the reliable lubricant supply to the raceway grooves.
According to another aspect of the present invention, the lubricant-containing members are fixed to the core metals by piercing the members with claws, which are formed by bending parts of the core metals or by implanting pins in the core metals. As an alternative, the lubricant-containing members are fixed to the core metals by grasping partially the members with grasping finger pairs, which are formed by bending parts of the core metals. Simply bending up tapered projections, which have been stamped out from the core metals, may form the claws to pierce the lubricant-containing members or the fingers to grasp the members. The sintered resinous components may be alternatively assembled to the core metal by mechanical means of pins that are implanted in the core metals.
Mechanical fixing of the sintered resinous components on the core metals makes it possible to ignore whether the immersion in the lubricant should be carried out after or before fixing the components on the core metals.
According to another aspect of the present invention, the lubricant-containing members are each fixed to the associated core metal on at least areas neighboring its portions which are brought into-sliding contact with the first raceway grooves on the track rail, irrespective of either adhesives or mechanical fixing. With regard to the accuracy in size of the lubricant-containing members, the portions in sliding contact with the raceway grooves on the track rail are very critical. The lubricant-containing members of this invention are each fixed to the associated core metal on at least areas neighboring its portions which are brought into sliding contact with the first raceway grooves on the track rail. Hence the lubricant-containing members may be prevented from the deformation at the portions that are in sliding contact with the raceway grooves, with keeping the highly accurate sliding contact relation with the raceway grooves.
In another aspect of the present invention, dustproof covers are disclosed for shielding the peripheries of the lubricant-containing members. The dustproof covers are provided so as to create no load acting on the lubricant-containing members to deform the members with respect to the track rail. The dustproof covers serve for keeping the lubricant-containing members from the contamination of the dust and dirt, preventing the lubricant-containing members from the breakage as well as the leakage of lubricating oil. The dustproof cover of a single member, when applied on the lubricant-containing members, has tended to cause such undue force as to urge the lubricant-containing member against the raceway grooves on the track rail. To cope with this, it is preferred to use a dustproof cover divided into two halves, each corresponding to each side section of the lubricant-containing member, or another dustproof cover to be fitted loosely over the lubricant-containing member, thereby eliminating the fear of undue force to urge the lubricant-containing member against the raceway grooves.
According to another aspect of the present invention, the end seals, lubricating plate assemblies and end caps are attached together to the casing by bolts. In connection with this arrangement, the lubricant-containing members in the lubricating plate assemblies are each provided with notches in alignment with holes in the associated core metal for the bolts, and collars are snugly fitted in the notches. Moreover, the collars fitted in the notches in the lubricant-containing members each have an axial length corresponding to the thickness of the lubricant-containing member whereby no clamp-down force created by the bolts acts substantially on the lubricant-containing members. In addition, the lubricating plate assemblies are each mounted between the associated end seal and end cap by the bolts in such a manner that the collars are abutted at their opposing ends against the end seal and the core metal. In some cases, the lubricant-containing members may be peeled off from the core metals for replacement by simply taking off the bolts. On mounting the lubricating plate assemblies with the bolts, the clamp-down forces created by the bolts may act on the core metals from the end seals through the collars and in turn be transmitted to the end caps, thus resulting in having little or no effect on the lubricant-containing members. This protects the lubricant-containing members from the deformation that might be otherwise caused owing to the clamp-down force at the portions made in sliding contact with the raceway grooves.
On the linear motion guide unit of the present invention, the core metals fixed to the lubricant-containing members by the adhesives or mechanical means may protect the members from the deformation, thereby maintaining accurately the clearance between the lubricant-containing member and the raceway grooves. The lubricant-containing members may supply smoothly the lubricant to the raceway grooves with no failure of lubrication, thereby helping ensure the good lubrication. The lubricant-containing members, as no urging force comes into action against the confronting raceway grooves, are reduced in sliding resistance to the track rail so that the sliding element may move nimbly on the track rail. The sintered resinous components for the lubricant-containing members may be easily formed with high accuracy of finishing within about xc2x10.025. This makes it possible to provide the components that are most suitable for the linear motion guide units incorporated into the precision machines. Since the sintered resinous components are formed with high precision while the lubricant-containing members are free from any urging force against the raceway grooves, the lubricant-containing members may be protected against wear as well as clogging up. The lubricating plate assembly of this invention may be simply mounted to the ends of the sliding element in the conventional linear motion guide unit, which has been incorporated in the machine tool and the like to thereby improve the self-lubricating performance of the linear motion guide unit.
Other objects and features of the present invention will be more apparent to those skilled in the art on consideration of the accompanying drawings and following specification wherein are disclosed preferred embodiments of the invention with the understanding that such variations, modifications and elimination of parts may be made therein as fall within the scope of the appended claims without departing from the spirit of the invention.